A fata morgana, the Italian name for Morgan le Fay, a main character of Arthurian legend, is a mirage, an optical phenomenon which results from a temperature inversion. Objects on the horizon, such as islands, cliffs, ships or icebergs, appear elongated and elevated.

In calm weather, the undisturbed interface between warm air over cold dense air near the surface of the ground may act as a refracting lens, producing an upside-down image, over which the distant direct image appears to hover. Fata morgana are usually seen in the morning after a cold night which has resulted in the radiation of heat into space. An early mention of the term fata morgana in English, in 1818, referred to such a mirage noticed in the Strait of Messina, between Calabria and Sicily. It is common in high mountain valleys, such as the San Luis Valley of Colorado, where the effect is exaggerated due to the curvature of the floor of the valley canceling out the curvature of the Earth. They may be seen in Arctic seas on very still mornings, or commonly on Antarctic ice shelves.

The ill-fated Crocker Land Expedition of 1913 was sent to map Crocker Land, a land mass in the Arctic Ocean that turned out to be nothing but a Fata Morgana.

Fata morgana is much more complex form of superior mirages, which are distinct from the more common inferior mirages. While with a simple superior mirage an observer sees an inverted image below the correct one, with fata morgana an observer would see complex alternation of distorted correct and inverted images.